Hardening furnace



Patented Feb. 9, 1937 UNiTED STATES PATET OFFICE HARDENING FURNACE cut Application August 13, 1936, Serial No. 95,794

1 Claim.

This invention relates to a furnace for hardening or heat treating articles of high speed steel and similar material.

The invention is disclosed in connection with a furnace of relatively small size such as suitable for hardening saw blades, and particularly hack saw blades, but the principles involved are not limited to the particular size of the furnace nor to the particular articles to be treated therein.

In the hardening or treatment of high speed steel and similar material in furnaces of this type, it is customary to dip the articles such as the hack saw blades in, or coat them with, borax or other suitable salt. During the heat treatment the hack saw blades or other articles are brought to and maintained at a high temperature, often well over 2000 F., and as a result the borax or salt, brought by the heat into a liquid state, drips off and accumulates on and adheres to the bottom of the furnace at the hardening chamber.

7 a furnace construction which will enable the accumulation of the borax or other salt adhering to the bottom of the hardening chamber to be frequently and readily removed at small expense and with little lost time.

The invention has thus for its further object to provide a removable bottom for the hardening chamber in which the articles to be hardened or treated are located, properly supported in position and capable of being readily cleaned and replaced.

The nature and objects of the invention will appear more fully from the accompanying description and drawing and will be particularly pointed out in the claim.

The drawing illustrates the main elements of a gas-burning furnace of a type suitable for hardening and treating high speed steel hack saw blades and disclosing a preferred form of the present invention with features of the furnace not essential to the present disclosure orriitted.

In the drawing:

Fig. 1 is a view in vertical cross section of the furnace.

Fig. 2 is'a top plan view of the removable bottom.

The furnace illustrated comprises essentially an outer heating chamber l and an inner concentric hardening chamber 2 separated by a muffle 3 of suitable material such as carborundum. The

shape, dimensions and size of the furnace may obviously vary according to the requirements. In the illustration the furnace is of a cylindrical shape.

The annular heating chamber l is provided with thick walls of refractory material, the main wall i surrounding the chamber and the wall 5 forming the bottom of the chamber. In the usual construction the wall 5 extends continuously across and forms also the bottom of the hardening chamber 2 and it is on this wall that the borax or other salt collects.

The furnace is heated in any suitable manner and, in the type illustrated, usually by gas jets located in the heating chamber and impinging against the muffle. A suitable removable plug 6 in the wall 4 gives access for lighting to the heating chamber l and a thermo-couple 1 enables the temperature in the hardening chamber to be ascertained.

The upper end of the furnace is provided with the usual refractory wall 8 and removable cover 9.

In the construction of this invention, the bottom wall 5 of the heating chamber terminates with the muffle 3 so that the hardening chamber 2 extends entirely through the bottom of the furnace. An independent bottom it) of suitable refractory material is removably supported against the bottom wall 5 and, extending beneath the hardening chamber 2, forms the bottom of this chamber. This independent bottom 10 is preferably of a somewhat saucer shape and presents a flat surfaced rim ll fitting snugly against the lower surface of the bottom wall 5. The surface of this independent removable bottom is provided with a thin coating I2 of clay on its surface onto which the borax or other salt falls and thus may readily be removed therefrom.

The independent removable bottom Ill is supported or clamped against the bottom wall of the furnace by a plurality of wedges l3 resting upon the surface I 4 upon which the furnace stands and engaging the periphery of the removable bottom.

Preferably the joint between the removable bottom and the bottom wall of the furnace is protected by a cement seal. l5 applied after the removable bottom' has been clamped in place.

The furnace is shown set up ready for use. With this construction the bottom of the hardening chamber may be readily cleaned as often as desired. When in constant use, it is desirable each day to remove the bottom, scrape off the collection of borax or other salt and replace the bottom. The whole operation requires but a few minutes of time.

Having thus described the invention, what is claimed as new, and desired to be secured by Letters Patent, is:

A furnace for hardening high speed steel and similar materials having concentric outer heating and inner hardening chambers separated by a mufiie, refractory walls at the bottom of and surrounding the heating chamber, an independent bottom of refractory material fitting against the bottom wall of the heating chamber and forming the bottom of the hardening chamber, and a plurality of Wedges beneath the removable bottom for supporting and clamping it against said bottom wall.

WILLIAM BENNETT STURGES. 

